Osteosynthesis devices of the type described hereinabove are used for stabilization of the spinal column of a human or animal body, in particular, if a vertebra or an intervertebral disk is damaged. For this purpose bone anchoring elements, for example, bone screws, are fixed on the vertebrae which are to be linked with the osteosynthesis device. In a next step a connection member, for instance, a rod, is inserted into the retainers or receptacles provided on the bone anchorage elements for receiving the connection member. After insertion of the connection member in the retainers of both anchorage elements, the connection member has to be fixed on the bone anchorage elements. It is known to use fixation screws for this purpose which can be screwed into threaded sections, for example, of heads of the bone anchorage elements. Inserting and tightening the fixation screws on the bone anchorage elements is difficult, even if the patient's body is widely opened for implanting the osteosynthesis device.
Obviously introducing such a fixation screw into the patient's body, inserting the fixation screw into the threaded section of the bone anchorage element and tightening the same in order to fix the connection member to the bone anchorage element are difficult and require enhanced skills on the part of the surgeon, in particular, if this procedure is to be carried out using a minimal invasive access to the patient's body.
The object underlying the invention is, therefore, to provide an improved surgical instrument and an osteosynthesis device of the type described hereinabove, which allow facilitated implanting of the device using a minimal invasive access to the patient's body. Moreover, it would be simpler and easier if a method were available for fixing the osteosynthesis device onto vertebrae of a spinal column in a minimal invasive manner.